Diversity of plant parasitic nematodes associated with common beans (Phaseolus vulgaris) in the Cent

Int. J. Agron. Agri. R.

International Journal of Agronomy and Agricultural Research (IJAAR) ISSN: 2223-7054 (Print) 2225-3610 (Online) http://www.innspub.net Vol. 12, No. 1, p. 62-68, 2018 OPEN ACCESS

RESEARCH PAPER

Diversity of plant parasitic nematodes associated with common beans (Phaseolus vulgaris) in the Central Highlands of Kenya J. W. Waceke*

Department of Agricultural Science and Technology, Kenyatta University, Nairobi, Kenya Article published on January 30, 2018 Key words: Meloidogyne, Pratylenchus, Gall index, Disease severity, PPN densities

Abstract Common beans (Phaseolus vulgaris L.) are the most important legume staple food in Kenya coming second to maize. In Central Highlands of Kenya, the 0.4-0.5ton ha-1 output is below the genetic yield potential of 1.5-2ton ha-1 partly due pests and diseases. Plant parasitic nematodes (PPN) have been reported to cause yield losses of up to 60% on beans. Though bean production is important in the Central highlands of Kenya, information on PPN associated with the beans in the region is lacking. This study was therefore undertaken to establish the diversity of PPN associated with common beans and to assess the root knot nematode damage on beans in the region. The study covered 50 farms (32 in Kirinyaga and 18 in Embu Counties) distributed in eight localities namely Kibirigwi (L1), Makutano (L2), Kagio (L3), Mwea (L4) and Kutus (L5) in Kirinyaga County and Nembure (L6), Manyatta (L7) and Runyenjes (L8) in Embu County and covering three Agro Ecological Zones (AEZs); UM2 (L1, L2, L3 & L4), UM3 (L5, L7 & L8) and UM4 (L6) AEZs. Manyatta (L7) and Nembure (L6), had the highest and second highest gall indices, respectively, while Kibirigwi (L1), Makutano (L2) and Mwea (L4) had some of the lowest gall indices. The most common PPN in bean roots were Meloidogyne spp. Pratylenchus spp. and Scutellonema spp. with a frequency of 94.38%, 78.25% and 59.13%, respectively. This further confirm the importance of these nematodes in bean production systems. Upper Midland 3 (UM3) AEZs and UM4 had higher nematode population densities and diversity than UM2. Disease severity and nematode composition and distribution were notably low in the irrigated areas Kibirigwi, Kagio and Mwea compared to rain-fed areas such as Makutano, Nembure and Manyatta. * Corresponding

Waceke

Author: Waceke J.W  wanjohi.waceke@ku.ac.ke

Page 62

Int. J. Agron. Agri. R. Introduction

associated with common beans and assess the root

Common beans (Phaseolus vulgaris L.) are the most

knot nematode damage on beans in the Central

important legume staple food in Kenya providing up

highlands of Kenya.

to 65 percent of the country’s national dietary protein intake and 32 percent of caloric intake (Wortmann &

Materials and methods

Allen 1994). Due to their capacity to fix nitrogen they

Study Area

are frequently used in maize cropping systems as an

The study was conducted in Kirinyaga and Embu

intercrop and reduces dependence on inorganic N

Counties in the Central Highlands of Kenya. These

fertilizers (Rheenen et al., 1981). In the central

counties lie on the foot of Mt. Kenya at 1280 - 2500m

highlands of Kenya, though bean production is an

above sea level. The climate is cool and humid\sub-

importance economic activity where it covers over

humid with an annual mean temperature of 20-21ď‚°C.

40000 hectares and, the yield of 0.5ton

ha-1

is far

This region has a bimodal rainfall pattern with peaks

below the genetic yield potential of 2ton ha-1 (Katungi

in May and November and a hot dry spell between

et al., 2010). These low yields are attributed to low

January and April. Average annual rainfall for this

soil fertility, diseases and insect pests as revealed by a

area is 1250mm in the higher altitudes. In lower

study conducted in 2015 in parts of the region

altitudes the rainfall decreases and the rainy seasons

(Mwaniki 2015). The bean diseases were ranked as

become shorter. Soils are deeply weathered volcanic

the most important (87.5%), followed by low soil

types mainly andosols in Upper Midland 2 (UM2) and

fertility (52.5%), insect pests (50%), lack of quality

nitosols in Upper Midland 3 (UM3) and Upper

seed (17.5%), low market prices (12.5%) and erratic

midland 4 (UM4) agro-ecological zones (AEZ)

weather patterns (10%) (Mwaniki, 2015). Although a

(Jaetzold and Schmidt, 1983).

study on the distribution and population densities of PPN associated with beans in Western Kenya revealed

The study covered 50 farms (32 in Kirinyaga and 18

that PPN are a big threat to bean production (Karanja

in Embu Counties) distributed in eight localities

et al., 2003), studies conducted in the central

namely Kibirigwi (L1), Makutano (L2), Kagio (L3),

highlands of Kenya often overlook the impact on PPN

Mwea (L4) and Kutus (L5) in Kirinyaga County and

on beans production. In other regions, plant parasitic

Nembure (L6), Manyatta (L7) and Runyenjes (L8) in

nematodes have been reported to cause yield losses of

Embu County. The farms were concentrated in the

up to 60% with root knot nematodes being rated as

UM2 (L1, L2, L3 & L4), UM3 (L5, L7 & L8) and UM4

the most important (Talwana et al., 2016; Kavuluko et

(L6) AEZs where cultivation of bean is most common.

al., 2010; Kimenju et al., 1999). In addition to direct

Though bean production is mainly rain fed, farms in

pathogenic effects on plants, the nematodes act

three localities; L1, L3 and L4 irrigate their crops

synergistically with other plant pathogens and pests

since most of them are under Kibirigwi and Mwea

to form disease complexes that further impact

Irrigation Schemes. In most farms, beans were inter-

negatively on the crops. The nematodes also suppress

cropped with maize.

nodulation and therefore affect nitrogen fixation (Kimenju

et

al.,

1999).

Information

on

PPN

Sampling

associated with common beans in Central Highland of

Samples were collected in the middle of the short rain

Kenya is lacking. Further, due to the growing

season October - November 2015. Ten bean and soil

importance of bean production in the region, it is

samples per farm were taken at mid-season when the

imperative that a study be undertaken assess the

bean plants were in the early poding stage. The farms

diversity of PPN associated with beans in an effort to

were selected with the assistance of the County

applying sound management and control strategies.

Executive Committee (CEC) offices in charge of agriculture in the two counties. The plants were

This study was therefore undertaken to establish the

gently dug out with a hand hoe taking care not to

occurrence and diversity of plant parasitic nematodes

damage the roots. Soil adhering on the roots was

Waceke

Page 63

Int. J. Agron. Agri. R. gently shaken off into a plastic bag, then the root

(Hooper et al., 2005) Nematode suspension from the

system was separated from the shoot system and

tray was sieved through a 38m sieve every day for 3

cleaned before assessing the gall index and extracting

days. The nematodes were backwashed into a beaker

the nematodes. The soil samples for each farm were

and concentrated into a 20ml suspension and placed

1000cm3

in vials. Nematodes were enumerated under a

bulked, mixed thoroughly before taking a for nematode assays

dissecting microscope and density and frequency of occurrence determined.

Assessment of disease severity Nematode damage on the bean plant was assessed by visually rating the roots for galls using the Bridge and Page (1980) gall rating of 0-10 where 0= No knots on roots; 1= Few small knots that are difficult to find; 2=Small knots only but are clearly visible and main roots clean; 3= Some larger knots are visible and main roots clean; 4=Larger knots pre-dominate but main roots clean; 5=50% of roots infested and knotting on parts of main root and reduced root; 6=Knotting on main root; 7=Majority of main roots knotted; 8=All main roots knotted but few clean roots visible; 9=All roots severely knotted and plants usually dying and 10=All roots severely knotted and

Results and discussion Nematode galling index The most distinct symptom of nematode damage on the bean plants was root galling by Meloidogyne spp.

Root Knot nematode damage levels varied in the 8 localities with Manyatta (L7) and Nembure (L6), having the highest and second highest gall indices, respectively. Kibirigwi (L1), Makutano (L2) and Mwea (L4) had some of the lowest gall indices of 1.17, 1.25 and 1.3, respectively, that differed significantly (p<0.05) from those in locality 7. Farms in localities 3, 5 and 8 had gall indices of 1.5 (Fig. 1).

no root system and plant usually dead.

Extraction of Nematode from bean roots The cleaned root systems from each farm were cut into 1cm long pieces, were well mixed before taking two 5g sub samples. One sub -sample was oven dried for 72 hours at 60C while the second one was used for nematodes extraction using Maceration-Filtration method (Hooper et al., 2005). The nematodes were harvested after 48 hours and concentrated into 20ml in vial bottles. Nematode population from each sample was determined using a 1ml aliquot of a wellmixed

suspension

pipetted

into

a

Hawksley’s

nematode counter and enumerated under a Leica MS 15 dissecting microscope. Counting was repeated in three aliquots and the mean recorded. Nematodes extracted from the roots were expressed per gram dry root weight. Nematodes were identified to genus level using the morphological features. A photographic record of the nematode genera was obtained using a digital camera (Leica DFC 280) mounted on a

‡ Gall

index according to Bridge and Page (1980) galling

scale of 0-10 where 1= No galls; 2=1-5%; 3=6-10%; 4=1120%; 5=21-30%; 6=31-40%; 7=41-50%; 8=51-75% and 9=76% of root system and 10=All roots severely knotted and no root system and plant usually dead.

Fig. 1. Mean Gall indices‡ on bean roots from farms in eight localities of Kirinyaga and Embu Counties.

The significantly higher RKN gall indices Manyatta could be due to the mixed crop farming (beans, tomatoes, squash, egg plants) that is a common practice in the area with most of the crops grown

compound microscope.

being good hosts to root knot nematodes (Silva dos Nematode extraction from the soil Nematodes were extracted from a

Santos et al., 2012; Waceke & Chege In Press; sub-

Weselmael & Maurice 2012). Further, the high RKN

samples using the Modified Extraction Tray method

disease severity in Manyatta and Nembure could be

Waceke

200cm3-soil

Page 64

Int. J. Agron. Agri. R. attributed to the susceptibility of the bean varieties

to the build -up of nematode levels over the seasons

grown in the areas. GLP 2 (Rose coco), GLP24 and

beyond damage thresholds (Omwega et al., 1989). In

GLP1004 bean varieties that are commonly grown in

farms where fertilizers (organic or inorganic) were

the area are more susceptible to RKN than GLP 585

used, lower gall indices were recorded. It has been

(Wairimu) and GLP 92 (Mwitemania) (Omwega et al.,

reported that application of organic amendments and

1989; Silva dos Santos et al., 2012; Weselmael &

fertilizers increases growth and vigor of nematode

Maurice 2012) grown in other localities. The relatively

infected plant thus allowing the host to tolerate

low galling indices some localities could be due to the

nematode attack (Rheenen et al., 1981) while organic

relatively poor bean host of RKN namely GLP 585

matter in the soil allows nematode antagonists to

(Wairimu) and GLP 92 (Mwitemania) that are grown

compete successfully and attack nematodes (Waceke

in the area besides the high use of pesticides and

and Waudo 2002).

organic and inorganic fertilizers. Farming in these localities is semi â&#x20AC;&#x201C; commercial unlike in other areas

Diversity and Density of PPN associated with beans

where farming is purely subsistence.

roots The

most

common

plant

parasitic

nematodes

The high nematode damage and population densities

encountered in bean roots were Meloidogyne spp.

could be due to poor agricultural practices (low or no

Pratylenchus spp. and Scutellonema spp. with a

fertilizer or agricultural inputs and continuous bean

frequency

cropping (twice a year)) in the areas. This contributes

respectively (Table 1).

of

94.38%,

78.25%

and

59.13%,

Table 1. Percent Frequency of occurrence of plant parasitic nematodes in bean roots obtained from 8 localities in Kirinyaga and Embu Counties.

Nematode genus Meloidogyne Pratylenchus Scutellonema Hemicycliophora

Kibirigwi 100 80 26

Makutano 100 86 63 -

Kagio 100 88 24 21

Mwea 78 37 62 -

Kutus 98 93 90 -

Nembure 85 84 74 -

Manyatta 100 80 80 -

Runyenjes 94 78 80 -

Hemicycliophora spp was present in two localities;

nematodes than lesion nematodes (Waceke et al.,

Kibirigwi and Kagio with a frequency of occurrence of up

2007; Waceke and Chege 2017 In Press).The

to 26%. Meloidogyne, Pratylenchus and Scutellonema

relatively high densities of Pratylenchus in Nembure

spp. have been reported to be the major nematode

could be attributed to the presence of coffee and

genera associated with beans in different parts of the

maize in most of the farms where beans were

country and so the findings of this study corroborates

intercropped with them (Waceke and Arim 2017; Arim

with the findings by Kimenju et al., 1999.

et al., 2006; Katungi et al., 2010). Coffee and maize are good hosts of Pratylenchus spp and coffee being a

Roots

of

bean

supported

higher

densities

of

perennial crop, it support the continuous growth and

Meloidogyne spp than Pratylenchus spp.in all the

reproduction of the lesion nematodes. Further, lesion

localities except Nembure where the density of lesion

nematodes are polyphagus except P. goodeyi which

nematodes was more than double that of the root

infects

knot nematodes (Table 2). The differences in the

ectoparasites; Scutellonema and Hemicycliophora on

densities of the two nematodes in bean roots could be

bean production needs to be further investigated.

only

bananas.

The

impact

of

the

two

attributed to the difference in their mode of feeding (lesion nematodes are migratory endoparasites while

Overall farms in Kutus, Runyenjes and Manyatta had

root knot nematodes are sedentary endoparasites and

some of the highest nematode densities in bean roots

to the susceptible bean genotype. The bean genotypes

while Mwea, Kibirigwi and Kagio had some of the

grown in the area are more susceptible to root knot

lowest densities (Table 2).

Waceke

Page 65

Int. J. Agron. Agri. R. Most of the farmers in the irrigation schemes

Disease severity and nematode composition and

concentrated in Mwea and Kibirigwi localities are semi

distribution were notably low in the irrigated areas (L1,

commercial farmers and use pesticides, organic and

L3 and L4) compared to rain-fed areas (L2, L5, L6, L7

inorganic fertilizers and practice good crop husbandry in

and L8). This supports the observation that disease

their production systems that could have reduced the

severity is more pronounced under conditions of water

nematode population (Wortmann & Allen 1994).

stress (Rheenen et al, 1981; Wortmann & Allen 1994).

Table 2. Mean Nematodes densities per g dry root weight of bean root in 8 localities in Kirinyaga and Embu Counties.

Nematode genus Meloidogyne Pratylenchus Scutellonema Hemicycliophora Total

Kibirigwi 33.6 8.4 5.2 47.2

Makutano 76 16.6 13.8 106.4

Kagio 47 16.2 2.4 4.2 69.8

Diversity and density of PPN in soil Eleven

PPN

genera

Pratylenchus

spp.

Helicotylenchus Tylenchorynchus

namely and

spp.,

Kutus 113.4 29.8 20.6 163.8

Nembure 36.2 84 7.4 127.6

Manyatta 97.4 17.4 20.2 135

Runyenjes 104.8 34.8 12.8 152.4

spp, some of the most frequently encountered had an

Meloidogyne Scutellonema

Paratylenchus

spp.,

Mwea 18.4 12.6 6.8 37.8

Tylenchus

spp.

overall percent occurrence of 100%, 97%, 73% and 63%,

spp.,

respectively (Table 3). All the 11 genera were present in

spp.,

three of the localities; Kibirigwi, Kutus and Nembure.

spp.,

Hemicycliophora spp., Hoplolaimus spp., Trichodorus

This could be attributed to the diversity of the crops

spp. and Xiphinema were encountered in bean

grown in these localities (Katungi et al., 2010). Kagio

rhizosphere soils (Table 3) underscoring the importance

had the lowest diversity of nematodes with seven out

of PPN in crop production systems. Pratylenchus spp,

of the 11 genera being isolated from the farms in this

Meloidogyne spp, Scutellonema spp and Paratylenchus

locality (Table 3).

Table 3. Percent frequency of occurrence of PPN in soil obtained from 8 localities in Kirinyaga and Embu Counties.

Nematode genus Meloidogyne Pratylenchus Scutellonema Helicotylenchus Paratylenchus Tylenchohynchus Tylenchus Hemicycliophora Hoplolaimus Trichodorus Xiphinema

Kibirigwi 100 100 70 80 50 70 81 31 33 72 30

Makutano 100 100 63 38 78 25 18 16 24 17

Kagio 100 100 51 23 50 22 50

Mwea 78 100 78 22 57 38 12 36 20

Kutus 100 100 81 82 46 82 48 63 46 100 65

Nembure 100 100 78 62 60 40 79 15 23 62 38

Manyatta 100 100 80 40 80 62 60 60 63 19

Runyenjes 100 100 60 21 81 42 96 40 43

Six of the 11 genera; Meloidogyne, Pratylenchus,

The three localities in Embu (Nembure, Manyatta &

Scutellonema, Helicotylenchus, Paratylenchus and

Runyenjes) had some of the highest nematode

Xiphinema

farms

densities in the soils and nematode diversity (Table 3)

underscoring the importance of PPN in agriculture. The

while Kagio and Mwea had some of the lowest

rich biodiversity could be due to mixed cropping systems

densities (Table 4).

were

encountered in all

the

in most of the localities (Kavuluko et al., 2010).

Table 4. Mean population densities of dominant plant parasitic nematodes recovered from 200cm3 of soil samples.

Nematode genus Meloidogyne Pratylenchus Scutellonema Paratylenchus Helicotylenchus Total

Waceke

Kibirigwi 266 272 38 34 80 690

Makutano 227 224 75 74 43 643

Kagio 184 201 28 29 11 453

Mwea 158 175 60 37 8 438

Kutus 264 222 77 27 72 662

Nembure 838 491 155 101 72 1657

Manyatta 602 359 174 97 18 1250

Runyenjes 487 285 69 92 14 947

Page 66

Int. J. Agron. Agri. R. The high nematode densities in these areas could be

The study revealed high densities of lesion nematodes

attributed to the mixed cropping practiced in the

(Pratylenchus

area while the low nematode densities in Kagio and

(Meloidogyne spp) in bean roots and soil. Upper

Mwea could be attributed to the application of

Midland 3 (UM3) AEZs and UM4 had higher nematode

pesticides and other inputs. Crop production in this

population densities and diversity than UM2. Disease

area is done on a semi- commercial basis and so

severity and nematode composition and distribution

application of pesticides and other inputs is

were notably lower in the irrigated areas compared to

relatively a more common practice than in other

areas where bean production relies on rain

spp.)

and

root

knot

nematodes

study areas. Some of the farms in these areas were formerly rice paddies and therefore the flooding

Recommendation

previously done could have contributed to the low

Continuous production of susceptible bean varieties

nematode densities. It is notable that these areas

should be minimized to reduce PPN population build

had also the lowest nematode diversity (Table 3).

up and minimize the detrimental effects on the beans.

Further selection of the varieties to be grown in the

High counts of lesion nematodes (Pratylenchus spp.)

area should be done carefully. Appropriate measures

recovered from both the soil and root samples further

should be incorporated in the bean production

confirm their association with bean plants. (Wortmann

systems to reduce the high densities of lesion

& Allen 1994)). Scutellonema spp., found in most of the

nematodes (Pratylenchus

localities is a polyphagous genus associated with a wide

nematodes (Meloidogyne spp).

range of plant species including maize and beans (Rheenen et al., 1981). Dominance of Meloidogyne species in all the localities may be attributed to the presence of beans, a suitable host and other alternative hosts (including weeds) and continuous cropping. The wide diversity of nematodes identified from the sampled farms could be due to mixed cropping systems (Rheenen et al., 1981).

and

structure

knot

Acknowledgement I acknowledge the Rockefeller Foundation for funding this project, the farmers for allowing the collection of samples from their farms and Kenyatta University for providing office and laboratory spaces.

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